1. Field of the Invention
The present invention relates to an energy recovery driver circuit for alternating current plasma display panel (hereinafter xe2x80x9cAC-PDPxe2x80x9d), and more particularly to an energy recovery driver circuit for the AC-PDP with a high energy recovery efficiency and an excellent property of enabling shorter rise-fall period of the voltage applied to the electrodes.
2. Description of the Prior Art
An AC-PDP is a graphic display panel of a new concept, utilizing plasma produced by gas discharge. An AC-PDP generally comprises a pair of 3 mm thick glass substrates formed with appropriate electrodes, coated with a fluorescent material and provided with a 0.1xcx9c0.2 mm space therebetween for producing plasma. Accordingly, an AC-PDP may form a bigger panel compared to LCD or FED, but due to the high driving voltage requirement and complicated input wave-forms, large power consumption and high costs are inevitable.
There are various driving methods of AC-PDPs according to the manner in which the driving pulses applied unto the pixels, i.e., addressing pulse, writing pulse, sustain pulse and erase pulse, are combined.
To realize color gray scales, a large number of sustain pulses are required, and the more the sustain pulses are provided, the better brightness the pixels will have. For example, to display 60 frames utilizing 256 gray scales per second with a unit level of four sustain pulses, 61,440 sustain pulses have to be applied unto the pixels and this predominates the total AC-PDP power consumption.
The sustain pulses are produced by two types of electrodes, one type of which produces voltages higher than the other type does and the voltage level difference is determined within the range of 140V to 200V.
Whenever these sustain pulses are applied unto each individual cell of the AC-PDP, displacement current corresponding to reactive power will flow. The moment the added amount of the wall voltage and the external voltage exceed the discharge threshold voltage, a discharge current will flow, thereby producing plasma discharge.
Sustain discharge is initiated only when certain condition inside a cell are satisfied. But, even when the conditions are not sufficient to produce plasma within a cell, the displacement current is to be constantly introduced into the individual cells, while the discharge current would not flow. The amount of displacement current is determined by the characteristic capacitance (Cp) inherent in a pixel which will be dependent on its structure and material. Reactive power consumed by the characteristic capacitance predominates the total power consumption.
Accordingly, extensive researches have been conducted to reduce the reactive power consumption and the circuit employed for such a task is called a energy recovery driver circuit.
Two types of electrodes are employed in each set of cells, facing each other wherebetween sustain discharge is performed by applying high voltages. If one type of the electrodes are defined as X, the X electrodes of the first set of the cells may be defined as X1 and the second set as X2. Similarly, if the other type of electrodes are defined as Y, the Y electrodes of the first set of the cells may be defined as Y1 and the other set as Y2. The conventional Weber method requires a separate energy recovery driver circuit corresponding to the energy recovery portion for each of the X1, X2, Y1 and Y2 electrodes.
FIG. 1 is a schematic diagram of an energy recovery driver circuit utilizing the conventional Weber method. FIG. 3 is a schematic diagram of an example of the Weber method energy recovery driver circuit wherein a tri-electrode planar discharge type AC-PDP is divided into two blocks to be driven separately.
The Weber type energy recovery driver circuit shown in FIG. 1 is operated as follows: Initial state is that all the switches of the side 1 sustain driver are open and the switch SW4 of the side 2 sustain driver is closed. And, the voltage level of each electrode is 0V. When the switch SW1 of the side 1 sustain driver is closed, electric charges stored in the capacitor Css, with the boost from the inductor L, flows into the PDP electrodes, thereby raising their voltage level. When the voltage level reaches its peak, the switch SW3 is closed and an increment of the voltage Vs is added to the PDP electrode voltage. Accordingly, a sustain discharge occurs in the AC-PDP and a discharge current flows through the AC-PDP into the switch SW4 of the side 2 sustain driver 2. Then the switch SW1 is open and the switch SW3 is open, too.
When the switch SW2 is closed at this state, electric charges present at the PDP electrodes move towards the capacitor Css through the inductor L and the switch SW2. When the PDP electrode voltages reach their minimum, the switch SW4 is closed, thereby dropping the PDP electrode voltages to 0V.
The Weber method explained above, however, requires independent inductors, many switches and diodes for the respective driver circuits and this creates much complexity in structure. Moreover, to enhance the energy recovery efficiency, longer time period for voltage rise and fall is required, thereby making it difficult to accomplish a short period of time for voltage rise and fall and at the same time a high energy recovery efficiency.
FIG. 2 is a schematic diagram of an energy recovery driver circuit utilizing the conventional Sakai method. The Sakai method is for an energy recovery method of utilizing exchange of voltages applied at two electrode groups wherein sustain discharge is produced by the manipulation of the switches SW1xcx9cSW6. In this circuit, energy recovery circuits are respectively arranged between two sustain driver circuits for X1 and Y1 electrodes and also X2 and Y2 electrodes.
However, the Sakai type energy recovery circuits also have the disadvantage of decrease in the energy recovery efficiency for shorter rise and fall period of applied voltage. These voltage rise and fall characteristics are similar to those of the Weber method and the energy recovery efficiency may differ only a little according to the circuit characteristics.
One object of the present invention is to provide an energy recovery driver circuit for the AC-PDP having an enhanced energy recovery efficiency with a short voltage rise and fall period by solving the above mentioned problems.
The energy recovery driver circuit for the AC-PDP according to the present invention, for the purpose of driving a pair of the AC-PDP cell groups, provides an energy recovery driver circuit which comprises an energy recovery part interposed between the sustain driver circuits for the X1 and X2 electrodes and the other energy recovery part interposed between the sustain driver circuits for Y1 and Y2 electrodes, wherein X1 and Y1 electrodes are respectively defined as electrodes of a first and a second type of electrodes employed in the first AC-PDP cell group, and X2 and Y2 electrodes are respectively defined as electrodes of the first and the second type of electrodes employed in the second AC-PDP cell group. Thus the energy recovery circuit of the present invention utilizes the effect of reducing the load capacitance to a half of its original value, when two (2) loads are serially connected.